Arch Cardiol Mex 2012;82(2):91-92

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EDITORIAL COMMENT Can we study the baroreflex mechanisms with other variables than blood pressure and heart rate? ¿Podemos estudiar los mecanismos barorreflejo con otras varia- bles de la presión arterial y la frecuencia cardiaca?

Received on March 20, 2012; accepted on March 30, 2012.

he baroreflex (BR) is a fundamental physiological The high pressure baroreceptors discharge during the mechanism that keeps the blood pressure (BP) sta- stretching of the walls of the arteries (loading of the re- ble by buffering the disturbances that arise in the flex) and decrease or abolish its discharge rate during T 1 system during the activities of the daily life. These dis- the collapse of the walls or decrease of the lumen of the turbances alter the control system and deviate the mean arteries (unloading of the reflex). During the loading of BP either increasing or decreasing it. The BP is maintai- the reflex the cardiovagal system is activated, whereas ned tonically around a “set point” and the disturbances during the unloading of the reflex the cardiosympathetic oscillate around it; they me be profound or relatively and vasoympathetic systems are activated.5,6 minor.2 Sometimes the disturbances occur at predictable The BP system is intrinsically “noisy” and there are times such as those seen during non-Rem sleep or rhyth- external and internal disturbances constantly acting on mic breathing.3 The disturbances could be considered the system requiring dampening or buffering of these “phasic” changes that are randomly added or subtrac- signals.5,7,8 The external disturbances including, changes ted to the tonically maintained set point. The set point from the supine or sitting to the upright position, respira- is dynamic and changes according to the mean BP main- tory movements, changes in temperature, pain, straining tained during a determined period of time, computed, and others. Internal disturbances are related to cognitive perhaps, in hours or days or even minutes.4,5 activities, emotions, voluntary muscle contraction, and It is a phylogenetically old mechanism that probably have been designated under the generic name of “central arose in the branchial arteries of the cyclostome fish.5 commands”.5, The baroreceptor reflex is a polysynaptic The BR is a negative feedback system composed in the reflex but the cardiovagal reflex is faster than the- car afferent side of high pressure baroreceptors located at diosympathetic and vasosympathetic reflex. These diffe- the carotid sinus and the aorta and a central mechanism rent time constants impose different types of oscillations whose putative integrative centers are located at the to the system.1-3.5 medulla in the nucleus of the tractus solitarii (NTR).1- The baroreceptor reflex has been studied for a number 5 The effectors of the reflex in the heart are the sinus of years by determining the relationship of the change in node, the conduction system and the ventricular system. systolic BP to the change of the RR intervals observed At the heart level may influence heart rate and contrac- in the ECG or in the interbeat interval (IBI). When the BP in- tility (stroke volume, SV).5,6 At the blood vessel level it creases the heart rate (HR) decreases (+BP-HR) (cardio- may constrict the arteries, the arterioles and the venous vagal reflex) and when the BP decreases the HR increases system. It has one vagal arm and one sympathetic arm to (-BP+HR) (cardiosympathetic reflex). The relationship of the heart, whereas the arm to the resistant blood vessels the BP to the HR has been termed barorereflex sensitivity is only sympathetic.5-8 index (BRS) and is measured as the ratio of IRRs measured

1405-9940/$ - see front matter © 2012 Instituto Nacional de Cardiología Ignacio Chávez. Publicado por Elsevier México. Todos los derechos reservados. 92 Estañol B in ms divided by the BP changes measured in mmHg: References ms/mmHg.2-7 This relationship has been evaluated with 1. Martínez-García P, Lerma C, Infante O. Relation of the baro- great many maneuvers including pharmacologic manipu- reflex mechanism with the photopletymsographic volume in lation, leg and neck suction and others and also during healthy young humans during orthostatism. Arch Cardiol Mex 2-7 “spontaneous sequence” changes. In this issue of Archi- 2012;82:(this volume). vos de Cardiología de México, Martínez P et al. propose 2. Di Rienzo M, Castiglioni P, Parati G. The sequence technique revised: a novel variable to be used in the evaluation of the BR Additional concepts on the assessment of spontaneous baroreflex function. The proposed variable is the photopletysmogra- function. Conf Proc IEEE Eng Med Biol Soc 2010;2010:1703-1705. phic volume or pulse volume (PV). The PV is measured 3. Oka H, Mochio S, Yoshioka M, et al. Evaluation of baroreflex sen- using the amplitude of the systolic pulse and can be used as sitivity by the sequence method using blood pressure oscillations and R-R interval changes during deep respiration. Eur Neurol a dependent variable. The authors measured the BRS 2003;50:230-243. with the sequence technique and the effect of systolic 4. La Rovere MT, Pinna GD, Raczak G. Baroreflex sensitivity: measu- BP on the PV also with the sequence method and with rement and clinical implications. Ann Noninvasive Electrocardiol spectral techniques.1 The authors demonstrated a signi- 2008;13:191-207. ficant correlation in the frequency domain at 0.04-0.14 5. Karemaker J, Wesseling KH. Variability in cardiovascular control: Hz “sympathetic frequencies” between the PV and the the barororeflex reconsidered. Cardiovasc Eng 2008;1:23-29. systolic BP during the upright position (orthostatism). 6. Bernardi L, Spoallone V, Stevens M, et al. Methods of investiga- The PV signal was obtained with an infrared photo- tion for cardiac autonomic dysfunction in human research stu- dies. Diabetes Metab Res Rev 2011;27:654-664. pletysmograph that is relatively inexpensive and this 7. Yasumasu T, Abe H, Oginosawa Y, et al. Assessment of cardiac signal was added to a channel of the Finometer. The baroreflex function during fixed atrioventricular pacing using measurement of the PV signal is easy and precise but it baroreceptor-stroke volume reflex sensitivity. J Cardiovasc Elec- is measured in a non physiological unit either as mm or trophysiol 2005;16:727-731. microvolts. The cross correlation is high with the blood 8. Hall JE. Guyton and Hall. Textbook of Medical Physiology, 12th. pressure. In my view, this represents a significant advance Philadelphia. Saunders. 2011. 220-230. in the understanding of the autoregulation of BP and may be applied to a number of diseases in which the heart Bruno Estañol rate is fixed or its variability is significantly decreased. Head of the Laboratory of Clinical Neurophysiology, The authors conclude: “The sequence method showed National Institute of Medical Sciences and Nutrition, a strong baroreceptor reflex upon peripheral blood vo- Mexico City, Mexico. lume that became more apparent during orthostatism”. Vasco de Quiroga # 15, Tlalpan, Mexico City. Whether the PV represents vasomotion or it also has a E-mail address: [email protected] component related to the stroke volume (SV) remains to be studied in the future.